Assemblers often assume that the board and component suppliers provide them with clean product. This was not a problem when everyone used water washable fluxes, because the water washing used to clean the flux residues also cleaned the board and components.
No-cleaners can not be so blase, because they never clean these components. They need to monitor the ionic contamination on their in-bound material. This becomes urgent where there's ionic material, humidity, and a bias voltage; the three factors that affect dendrites.
Water soluble fluxes leave ionic residue detectable by: * ROSE testing (ie, Omega meter, Ionograph....). This test is useful to determine whether the cleaner is in control. Commonly used throughout the industry. * Ion chromotagraphy. This test determines what specific residue causes failure. Only large shops can maintain the equipment. So, generally, smaller shops use outside laboratories. * Surface Insulation Resistance. This test actually has a correlation with field failures. None relating to residue if resistivity is above a certain level. Guaranteed if its below a certain level. The level depends upon environment, panel design and circuit design (voltage, current, impedance, spacing, indoors vs. under the hood...). This test should be done on test coupons in an environmental test lab. It is rarely done as a process control, since the test takes a week, and is not usually done on production panels.
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